The present invention relates generally to, an improved composite material comprised of a graphite fiber/aluminum matrix composite. More particularly the graphite fiber/aluminum matrix (hereinafter referred to as Gr/Al composites of this invention have been found to have marketly improved properties when coated with magnesium (Mg) vapor.
Advanced composite materials have in the past derived their usefulness and unique properties by incorporating high strength filaments, fibers or whiskers used as a reinforcement element in a metal matrix. These elements impart stiffness to the matrix. Through the combined behavior of the two constituents these genetic composite materials exhibit specific mechanical properties exceeding those of classical structural materials. Additional properties include higher service temperature capability and improved dimensional stability. With time these act as drivers for metal matrix composites usage.
Some metal matrix composite systems have very important properties, such as high temperature and high strength. Such a composite is the graphite fiber reinforced aluminum (Gr/Al). This composite has a great deal of potential usage in aero-space applications that requires improved strength to density and modulus-to-density ratios as compared to materials such as steel, aluminum and copper.
Several methods of Gr/Al composite fabrication have been attempted using liquid metal infiltration precursor wire.
For example in recent years electroplating and liquid infiltration as disclosed in Lachman et al. U.S. Pat. No. 3,894,863 has been attempted to produce Gr/Al composites.
In addition Sara U.S. Pat. No. 3,473,900 discloses tantalum coated carbonographite fibers bonded in an essentially aluminum matrix. In this system tantalum is used as a wetting agent.
U.S. Pat. No. 3,535,093 also issued to Sara and was drawn to and discloses the electro plating of silver on carbon fibers and then incorporates them into an aluminum matrix. This patent did not disclose graphite aluminum composites.
In recent developments, a chemical vapor deposition technique disclosed by Jackson, Braddock and Walker in the "Fiber Science Technology" volume 5, 1972--pages 219 to 236 is one method that has showed some promise in the production of composites of the graphite/magnesium type. In addition powder coating, plasma spraying, and sandwiching of foils have been attempted in the United States to produce Gr/Al composites. The only method among those attempted that has shown some potential of commercial success is the coating of graphite fiber yarn with titanium diboride by chemical vapor deposition followed by the liquid infiltration of aluminum. This process is disclosed by Praprocki in the carbon fiber reinforced metal matrix. Second conference on composites May 1978.
This process is quite limited, in that it requires an inert atmosphere throughout the entire process. The composite produced had a low transverse strength and demanded coating with additional aluminum foil before diffusion bonding to produce the final plates of Gr/Al composite.
Recently an ion-plating technique was used in Japan to produce a Gr/Al monolayer precursor tapes. These tapes were stacked together and hot pressed into plates by the Japanese. The composites produced had properties comparable to those prepared using the United States wire technology.
The Japanese produced a IPG/Al precursor product.
The IPG/Al monolayer precursor tape spools were obtained from Celeanese Corporation, Summit, N.J. An aluminum alloy matrix used for the IPG/Al tape was reported by the Japanese manufacturer to contain 5-6 weight percent magnesium.
Generally speaking, Gr/Al composites have been either unexceptable, too expensive or have processing properties that do not conform to those required by the industry.